The present invention relates to electronic musical instruments and more particularly, to electronic musical instruments such as electronic organs, electronic pianos, electronic accordions and the like based on a system wherein information of actuation of keys is detected by scanning the keys of a keyboard.
Conventionally, as a superior system for detecting information of actuation of keys and for memorizing and holding the information by extremely simple circuitry, there has been proposed an arrangement by the present inventor and others, for example, in Japanese Laid Open Patent Application Tokkaisho No. 52/143010, in which there is disclosed an electronic musical instrument which employs an extremely simple circuit stable for formation into a large scale integrated circuit (referred to as LSI hereinbelow) by arranging to "dynamically" memorize and hold the information of actuation of the keys in electrical capacity or capacitance corresponding to each of the keys. In the known arrangement as described above, the gate capacity of MOS (metal-oxide-semiconductor) type transistor is employed for the electrical capacitance, but in the system wherein variation in the envelope of musical note or tone is involved as in "sustain" function, sufficient time constant (normally required up to 1 to 3 seconds) is not available, and thus, it has been necessary to set the respective capacitances to considerably large values. Accordingly, incorporating or integrating the capacitances of large values as described above into the same chip together with other constituting elements (for example, the portion equivalent to FIG. 1 of Japanese Laid Open Patent Application Tokkaisho No 52/143010 mentioned earlier) results in a marked increase of area of the chip, with consequent high cost and reduction of yield in manufacturing to a large extent, thus not being suited to practical application. Furthermore, if it is intended to simultaneously use the same LSI for a musical instrument accompanied by the envelope variations as in "sustain" function and also for a musical instrument not accompanied by the envelope variations (i.e., musical instrument without the "sustain" function, etc.,) considerably wasteful portion not directly related to the intended functions is undesirably involved within the LSI, especially in the latter system not accompanied by the envelope variations, thus also presenting problems in the practical application.